The present invention relates to an antenna for transmitting and receiving radio frequency signals; and, more particularly, to a dual-band antenna for mobile telecommunication units, capable of operating in two frequency bands.
Nowadays, a variety of mobile telecommunication services is being commercially offered all over the world. While some of these mobile telecommunication services utilize a same frequency band by employing different modulating systems, the majority of these mobile telecommunication services in general utilizes frequency bands different from each other as exemplified by the cellular system and the personal communication system(PCS), the cellular system and the PCS system utilizing a frequency band of 824 to 894 MHz and 1.75 to 1.87 GHz, respectively.
A retractable antenna, in which a monopole antenna and a helical antenna are joined to each other and which is contractibly mounted on an upper portion of a mobile phone unit, is most widely used.
When the retractable antenna is extended out from the mobile unit, the monopole antenna operates independently or together with the helical antenna to transmit and receive a signal of a desired frequency band. When it is contracted in the mobile unit, only the helical antenna operates.
This retractable antenna, while suitable for operating only in one frequency band, is unsuitable for use in two or more different mobile telecommunication services, each telecommunication service operating in a different frequency band, while maintaining a desired radiation pattern. The reasons are as follows: Firstly, in order to make it possible for the antenna to operate at the frequency bands of both of the cellular system and the PCS, a complex matching circuit must be realized, matching a part or all of the bands, since a bandwidth between the cellular system and the PCS is in the neighborhood of 1 GHz; secondly, it is difficult to use one antenna for two different frequency bands since the central frequency of one mobile telecommunication frequency band is not a multiple of the harmonic component of that of the other mobile telecommunication frequency band; and thirdly, even if the antenna has been matched for use in two or more frequency bands, it is often difficult to realize a desired radiation pattern with the antenna at each of the frequency bands. In other words, in order to be serviced by a mobile telecommunication service, it is desirable for the customer to have a mobile phone unit designed for that particular frequency band thereof.
Therefore, in order to alleviate such a problem, a mobile phone unit, and hence, the parts therefor, capable of being used in mobile telecommunication services operating at different frequency bands, is desired.
There is shown in FIG. 1 a conventional dual-band helical antenna which operates in two frequency bands. As shown, the dual-band helical antenna includes a support 120 made of an insulating material and coils 130 and 140 wound on an upper part 100 and a lower part 110 of the support 120, respectively, thereby forming two helical antenna sections. The helical antenna sections are designed to have different resonance frequencies, respectively. Further, an inner portion of the support 120 is provided with a coaxial line. The number and a pitch of the windings and a length of a coil wound on a helical antenna section are different from those for the other helical antenna section in such a way that the two helical antenna sections are provided with two different resonance frequencies.
Therefore, when a voltage is applied through a coaxial line in the support 120, two helical antenna sections resonate at two different frequency bands, respectively.
However, the above described antenna has a shortcoming in that since the helical antenna is divided into the upper part and the lower part of the support, it is rather bulky and hence occupies a large space in the mobile phone unit, thereby posing an obstacle to current trend in mobile phone design of downsizing, i.e., to make the phone as light and as small as possible.
It is, therefore, an object of the present invention to provide a dual-band antenna for mobile telecommunication units capable of operating in two frequency bands.
Another object of the present invention is to provide a dual-band antenna for mobile communication units which is small in size.
In accordance with the present invention, there is provided a dual-band antenna for mobile communication units comprising a support made of an insulating material; double stranded helical conductors wound in an identical direction on the support without intersecting each other to have a first and a second resonance frequencies, respectively, a winding region of the second helical conductor being a part of that of the first helical conductor; and a coaxial feeder connected to an end of each of the helical conductors and for applying a voltage thereto.